The present invention relates to a printing apparatus provided with printing means, a carriage, and a holder, the printing means including a type carrier, such as a type wheel, and type selection means, such as a character selector motor, the holder supporting the type wheel and/or the type selection means and being movable relatively to the carriage.
FIGS. 1 and 2 show a conventional printing apparatus of this type. In printing a character or the like on a printing sheet 14 on a platen 1 of this apparatus, a carriage 3 is first moved along a guide shaft 2 and a printing line on the platen 1 to its printing point, with a holder 5 kept in a printable position indicated by the full line in FIG. 1. Then, a specific one of the type elements 7a on a type carrier 7, formed of a daisy wheel, is selected and opposed to the printing point on the platen 1, by means of a type selection motor 6 on the holder 5. The selected type element 7a is struck by a printing hammer 8a. The hammer 8a is operated by means of a hammer driver 8 which is supported on a top bent portion 5a of the holder 5. In replacing the type carrier 7, moreover, the holder 5 is moved from a printable position, where it is situated close to the platen 1, to a retracted position indicated by the two-dot chain line in FIG. 1. The holder 5 is also slidably mounted on the guide shaft 2. The type carrier 7 is mounted on a rotating shaft 6a of the motor 6.
In a printing operation, the selected type element 7a is struck against the printing sheet 14 on the platen 1 by the printing hammer 8a in a manner such that a ribbon 13 drawn out of a ribbon cassette 9 is interposed between the element 7a and the sheet 14. In shifting the holder 5 between the printable position and the retracted position, an operator holds and operates a shift lever 10 attached to the holder 5.
In the prior art printing apparatus described above, the holder 5, which is formed by pressing an iron plate, is provided with an integral coupling projection 11 having a guide groove 11a. The groove 11a, which is open at one end, extends at right angles to the carriage transfer direction. A raised piece 12 is formed integrally on one side of the carriage 3, which also is formed by pressing an iron plate. The raised piece 12 and the guide groove 11a constitute coupling means for connecting the carriage and the holder. As the piece 12 and the groove 11a engage each other, the holder 5 is allowed, to move between the printable position and the retracted position. In the carriage transfer direction, the holder 5 is moved in one with the carriage 3. Since the raised piece 12 is a thin plate, however, the engagement between its engaging portion and the guide groove 11a lacks stability. Thus, the raised piece 12 and the guide groove 11a are subject to play between them, so that the carriage 3 and the type element 7a are liable to be dislocated from each other. Part of a wire 4, which is used to apply a driving force to the carriage 3, is fixed to an anchor portion 3a located substantially in the center of the carriage 3 and off the raised piece 12. If the tractive force of the wire 4 is applied to the carriage 3 in the carriage transfer direction indicated by the arrow, the raised piece 12 may possibly bend, as indicated by the two-dot chain line in FIG. 2, due to the low rigidity of the piece 12, the force of inertia of the holder 5 and the type carrier 6 thereon, and frictional resistance between the holder 5 and the guide shaft 2. Accordingly, the dislocation between the carriage 3 and the holder 5, i.e., between the carriage 3 and the type element 7a, increases, so that the printing pitches become irregular, thus lowering the print quality.
Meanwhile, if the rigidity of the carriage 3 is increased by thickening its wall or by additionally providing a reinforcing member, in order to prevent the raised piece 12 from bending, the carriage 3 becomes heavier in weight. Thus, a drive source with a greater driving force must be used, possibly entailing an increase in manufacturing costs, as well as in size, and preventing high-speed printing operation.